High dose ion implants require high ion beam currents in order to maintain high implanter productivity. In the advanced technology integrated circuit fabrications, very low energy and high beam current implants are essential. Accurate implant angle and dose uniformities are becoming more and more critical as the technology nodes move towards 45 and 32 nm. However, prior arts ion implanter technologies cannot meet these requirements. Perveance is a term represents combination effects of ion beam current and energy on the beam transportation. The higher the ion beam current and the lower the ion energy are the larger is the Perveance value.
The large Perveance beam tends to be blowup during its transportation. Any electrostatic potential exists in the beamline that is for ion beam generation and transportation can severely limit beam currents to a target. This is because the potential push electrons inside the beam away to result positive space charges in the beam. The beam electrons are produced when energetic ions interact with the beamline residual gas atoms or molecular and they are trapped inside the ion beam to keep the ion beam positive space charge very low. Large space charges can be resulted if these electrons are stripped away from the beam. The positive space charges of ions tend to push the ions move laterally. The beam size can be quickly increased as it propagates so that the partial beam hits on the physical boundary of the beamline system before the beam reaches a target. Therefore, for a high perveance ion beam transportation it prohibits any electrostatic scanning mechanism, magnetic scans or stationary beams are used.
FIG. 1 shows a type of ion implantation system for silicon wafers and that is represented by the Models SHC 80, VIISta-80, and VIISta HC ion implantation systems manufactured by Varian Semiconductor Equipment Associates of Gloucester, Mass. This system is illustrated and adapted from FIG. 1 of U.S. Pat. No. 5,350,926. The disclosures made in U.S. Pat. No. 5,350,926 are hereby incorporated by reference. The system comprises an ion source 2 for generating an ion beam 1, an analyzing electromagnet 3, a resolving aperture 4, and a second electromagnet 5. A control unit 36 receives beam intensity information on line 36a from a beam profiler and sends control signals along line 36b to control multipole elements in magnet 3 or along line 36c to control a beam trimmer. Magnet 3 mass analyzes the ion beam. Magnet 5 expands the beam along the dispersive plane using magnetic fields in closed loop control to maintain the uniformity of the beam. The result is a ribbon-shaped ion beam 6 that is incident on target 7. Further details of the system of FIG. 2 are set forth in U.S. Pat. No. 5,350,926.
The major issue of this approach in generating and employing a ribbon beam is that the ribbon beam cannot be generated with uniform implant angle and also provide uniform implant dose. The beam intensity must be uniform in one direction. This beam intensity uniformity is obtained by moving some beam from high intensity regions to lower intensity regions so that the beam angle integrity is sacrificed because of beam intensity adjustments.
Another U.S. Pat. No. 5,132,544 discloses a system as that shown in FIG. 2 for irradiating the surface of a substrate with atomic or molecular ions by rapid scanning of a beam in two dimensions over the surface of the substrate. A scanning system is shown for deflecting the beam in two dimensions relative to a reference axis and a magnetic ion beam transport system following the scanning system is arranged to receive the beam from the scanning system over the range of two dimensional deflections of the scanning system and constructed to impose magnetic field conditions along the beam path of characteristics selected to reorient the two-dimensionally deflected beam to a direction having a predetermined desired relationship with the axis in the two dimensions at the desired instantaneous two dimensional displacement of the beam from the axis, to produce the desired scan of the beam over the substrate. One scanning system includes sequential first and second time-variable-field magnetic scanners, the first scanner having a magnetic gap of volume smaller than that of the second scanner and constructed to scan the beam more rapidly than the second scanner. In another system, the scanners are superposed. The magnetic ion beam transport system presently preferred is a system producing a sequence of three or more quadrupole fields, implemented by a sequence of quadrupoles. Alternate structures are disclosed. The system is capable of depositing atomic or molecular ions with a desired angular and positional uniformity over a wide range of perveance including perveance above 0.02/M[amu].sup.½ (mA//keV.sup. 3/2) with a constant, adjustable spot size and small beam spread.
In this approach the major problem is that beamline needs a lot of magnetic lens in order to make beam shape is proper for its magnetic scanning to work. Therefore, the beamline is very long for a beam's transportation. The lower beam currents are resulted because of long travel distances.
In another U.S. Pat. No. 7,235,797, an implanter is disclosed as shown in FIG. 3 that provides two-dimensional scanning of a substrate relative to an implant beam so that the beam draws a raster of scan lines on the substrate. The beam current is measured at turnaround points off the substrate and the current value is used to control the subsequent fast scan speed so as to compensate for the effect of any variation in beam current on dose uniformity in the slow scan direction. The scanning may produce a raster of non-intersecting uniformly spaced parallel scan lines and the spacing between the lines is selected to ensure appropriate dose uniformity.
FIG. 4 illustrates the problems of this beam scanning process. The target has to have mechanical scans in two directions. A lot of beam has to be implanted outside the target due to two-dimensional over scans. Especially, when the beam height is smaller than wafer diameter, two-dimensional mechanical scans with a wafer is held on a robot type of object that can move left/right and up/down to form beam implanted pattern must be carried out. In order to have sufficiently good implanted dose uniformity it needs many scans, which will require longer implant time. Also, mechanical turnaround in reciprocal motion can result a lot implant dead time. Therefore, this beam scanning process has very poor ion beam utilization and low productivities thus causing higher production costs and unnecessary wastes of energy and manufacturing resources.
For these reasons, there is a need in the art of integrated circuit fabrication to provide a new system to resolve the above-discussed difficulties. Specifically, there is a need for a new and improved systems to resolve the problems of the conventional types of ion implantation systems by providing a viable solution for perforthing one wafer at a time implantation with a high-current, high dose and angle uniformities.